1. Field of the Invention
The present invention relates to a couch positioning system for radiotherapy which irradiates an irradiation target with various radiations, such as X-ray or proton beam and other particle beams, to perform treatment. The present invention also relates to a treatment plan unit and a couch positioning unit.
2. Description of the Related Art
Radiotherapy intended to necrose tumour cells by irradiating them with various radiations has been widely performed in recent years. Radiations presently used for treatment include not only the X-ray, which is most widely used, but also proton beam and other particle beams.
One of the important processes of radiotherapy is couch positioning. Couch positioning generally refers to a process comprising the steps of: comparing a DRR (Digital Reconstructed Radiograph) image outputted from a treatment plan unit with an X-ray image (Digital Radiograph image or DR image) taken with a patient lying down on a treatment bed (hereinafter abbreviated to couch) by use of an X-ray imaging unit before radiation irradiation, by a therapist or a doctor; calculating a gap between the position of an irradiation target determined by a treatment plan and the present position of the irradiation target on the couch; obtaining the couch displacement so that the two images are in alignment; and moving the couch.
The DRR image, a simulated X-ray image, is generated from an X-ray CT image taken at the time of treatment planning. At couch positioning, it may be possible to use an X-ray perspective image taken by use of an X-ray simulator as well as the above-mentioned DRR image as a reference image.
Examples of a typical method of couch positioning include a method of marking reference points (calculation points) on the DRR and DR images, which will be explained below.
In order to obtain the couch displacement, an operator uses a couch positioning unit having a function to display a DRR image and an X-ray image side by side. The couch positioning unit is composed of: monitors for image display; operation units which perform positioning operations; and input means such as a keyboard, a mouse, or the like.
The operator inputs calculation points by use of certain input means in such a way that calculation points overlap characteristic points in the DRR image reflected on the monitor of the couch positioning unit and markers (metallic pellets, etc.) existing within the irradiation target, the markers being embedded before CT imaging at the time of treatment planning and reflected also in the DRR image. The operator likewise inputs calculation points also in the DR image. After inputting of calculation points, calculation points in the DRR image and calculation points in the DR image are converted to coordinates having, for example, the image center as an origin. Converted coordinates are compared with each other to calculate the couch displacement. This kind of method is disclosed for example in JP-A-2000-510023. Further, since the DRR and DR images respectively taken from the irradiation direction and a direction perpendicular thereto are generally used, a total of four images are required.